Recently, the Federal Communications Commission (FCC) has approved the operation of unlicensed radio transmitters in the broadcast television spectrum at locations where that spectrum is not being used by licensed services under certain restrictions. Some restrictions are specified in a publication by the FCC, entitled “Second Report and Order and Memorandum Opinion and Order,” ET Docket No. 08-260, November 2008. The unused spectrum available for unlicensed use, which may include television and other pre-allocated spectrum, is often termed “white space”. One major restriction on spectrum use is that unlicensed devices which can operate in the white space will be required to sense, at levels as low as −114 dBm, licensed transmitter signals, such as licensed digital and analog television transmitter signals, licensed wireless microphone signals, and signals of other services that operate in the multiple use bands on intermittent basis. In one example, a licensed sports television network may have authority to operate in the area of a sports arena, such as a football stadium. Such licensed use can include the use of wireless microphone transmitters to accommodate coverage of the sports event. However, such use is intermittent because the football event may only occur for a limited number of hours of an event day. Thus, the spectrum normally available only to the licensed wireless transmitters can be made available for un-licensed use under the new FCC guidelines.
Some prior art devices which detect white space frequency band availability operate on the principle of spectrum peak detection of licensed transmissions. However, such spectrum peak detectors will fail to properly identify an available channel when strong adjacent channel interference exists. Strong licensed signals, such as a digital television (DTV) signal can introduce adjacent channel interference due to leakage into adjacent spectrum which can cause false positive results in white space detectors that operate using spectrum peak-based detection. This false detection can eliminate an otherwise available channel from being utilized by the white space detector.